I have two parts cars and making one good one between them. I had my drivers seat recovered and installed it but the seat heater isn't working correctly.
When I turn it on, it comes on for about 3 seconds and then goes off. If I unplug the connector at the seat, it flashes on and off in less than a second.
I've confirmed the seat is the problem by swapping the seats around and the problem follows.

I'm looking for someone who knows how the seat controller works. I've ohmed out the good seat and I get 15K ohmes across the heater pins and 50 ohms across the resistor pins. When I ohm out the bad seat, I get 19K ohms across the heater and 50 ohms across the resistor pins.

So I'm guessing the controller needs to see a predicted current draw to operate. Too little and is shuts off immediately, too much and it overloads. Does anyone know what the ohm value range of a good seat is? I'm trying to decide if the resistor can be changed to bring the heater into ohm range. The attached drawing out of the Bently, shows it a 'variable resistor'. So it must be adjustable...

Any help would be appreciated.

 

Before I say anything, I want to let you know I don’t have all the knowledge you’re looking for and I’m hoping someone who has more expertise comes along.

I was recently trying to wire an aftermarket heated seat element to the stock switch. Once I realized there was a temperature sensor in the circuit that safely switches off the element should it become to hot, I decided to completely forgo the stock set up altogether. Reading about you’re issue where it comes on for a few seconds and itself off makes me wonder if the temp. sensor needs to be replaced.

Good luck solving this one. I’m going to stay tuned.

 

The variable resistor is actually a temperature sensor. The ohms change with temp and the controller calculates the temp from its value.
The behavior you describe - the heater coming on briefly and then shutting off - is typical of a bad temp sensor. It’s integrated into the seat bottom heating element. That’s the part you need to replace (or swap out from a good seat).